An electric double layer capacitor has a terminal portion for conducting inputting and outputting of an electric energy between an element assembly in the inside, and the outside. As the terminal portion, a terminal portion 10A of mold type has been known.
FIG. 6 shows a cross sectional view of a terminal portion of mold type.
In FIG. 6, the mold type terminal portion 10A has a sealing plate 11 in which a pair of terminals 12 and 13 are inserted vertically through the sealing plate, and they are molded to constitute a cap 15. Here, the sealing plate 11 is made of an insulative resin, and the terminals 12 and 13 are made of aluminum, and boundary portions 11a of the sealing plate 11 facing the terminals 12 and 13, and boundary portions 12a and 13a respectively of the terminals 12 and 13 facing them are provided with a labyrinth structure. This structure minimizes gaps between the sealing plate 11 and the terminals 12 and 13, formed by a thermal shrinkage difference between the sealing plate 11 and the terminals 12 and 13, due to the difference of their materials.
Further, to lower portions of these terminals 12 and 13, the respective lead wires 18 and 19 are connected to electrically connect the terminals with electrodes of the element assembly in the inside, not shown.
Further, in the cap 15, a notch 16 formed by circumferentially notching the outermost peripheral portion of the upper face side of the sealing plate 11, is provided. Then, in the notch 16, a seal member 17 made of a rubber having substantially the same shape as the notched shape, is fitted and bonded.
Further, in the uppermost end of the outer casing 21, a crimping portion 23 is provided. The crimping portion 23 is configured to be crimped inwardly to fix the upper side of the cap 15 with a seal member 17 sandwiched between them. Further, in the outer casing 21, a concave portion 24 in which the outer casing 21 is recessed inwardly, is formed at the position below the crimping portion 23 by about the thickness of the sealing plate 11, so that the concave portion 24 supports the underside of the cap 15.
In such a construction, since the terminals 12 and 13 are sufficiently distant from each other, and the sealing plate 11 is made of a resin, the terminals 12 and 13 are sufficiently insulated from each other. Further, since the terminals 12 and 13 are sufficiently distant from the outer casing 21, isolation is formed also between them. Accordingly, it is possible to prevent short circuit through a liquid or short circuit to the earth, of the electric double layer capacitor.
Here, as an electrolytic capacitor having substantially the same terminal portion as the terminal portion 10A, Patent Document 1 is known. Patent Document 1 shows a sealing structure effective for sealing a non-aqueous type capacitor element whose inside needs to be highly dehydrated.
However, in e.g. the above-mentioned terminal portion 10A or the terminal portion shown in Patent Document 1, even if a labyrinth structure is provided in the boundaries between the sealing plate 11 and the terminals 12 and 13, due to e.g. a difference in thermal expansion coefficient or thermal shrinkage coefficient between the resin material constituting the sealing plate 11 and the metal material constituting the terminals 12 and 13, it is difficult to completely prevent leakage of electrolytic solution through the gap between the sealing plate 11 and the terminals 12 and 13.
Further, the cap 15 of the terminal portion 10A is fixed to the outer casing 21 by crimping. However, since the outer casing 21 is usually made of aluminum, due to e.g. increase of internal pressure when the cell is used for a long time, crimping force of the crimping portion 23 is reduced, whereby there has been a risk that an electrolytic solution leaks out through the gap between the cap 15 and the outer casing 21. Additionally, there has been a risk that unnecessary materials are interfused from the outside.
For this problem, as a structure for preventing leakage of electrolytic solution through the gap between the sealing plate 11 and the terminals 12 and 13, a terminal portion 10B serving also as a terminal, has been known.
FIG. 7 shows a cross section of the terminal portion 10B serving also as a terminal. Here, elements in common with FIG. 6 are designated by the same reference numerals and explanations for these elements are omitted.
In FIG. 7, the terminal portion 10B serving also as a terminal, has a one-piece type cap 35. The one-piece type cap 35 is constituted by a sealing plate 31 corresponding to the sealing plate 11 of the mold type terminal portion 10A, and a terminal 32 corresponding to the terminal 12 (or terminal 13), formed in one piece, and these constituents are made of a type of metal. Accordingly, differently from the terminal portion 10A of mold type, the sealing plate 31 serves also as a terminal 2. Further, to the one-piece type cap 35, a lead 18 is connected to electrically connect with a terminal of an element assembly in the inside.
Here, in the one-piece type cap 35, besides a notch 16 circumferentially provided in the upper face side, a notch 36 formed by circumferentially notching the outermost peripheral portion of the lower face side of the sealing plate 31, is provided. Further, to the notch 36, an insulation member 37 is attached, and the insulation member 37 is arranged so as to encompass the side portion of the sealing plate 31.
Further, the one-piece type cap 35 has an upper face side fixed by a crimping portion 23 of the outer casing 21 by crimping, and a lower face side configured to be supported by a convex portion 24 with an insulation member 37 interposed between them. Here, the insulation member 37 is configured to be interposed also between the side portion of the sealing plate 31 of the one-piece type cap 35 and the outer casing 21.
In such a construction, since the sealing plate 31 and the terminal 32 are formed into one-piece member, leakage of an electrolytic solution or interfusion of unnecessary material through a gap between the sealing plate 31 and the terminal 32, can be prevented.
However, in such a terminal portion 10B, it is not possible to maintain the insulation distance between the sealing plate 31 and the outer casing 21, and there has been a risk that short circuit through a liquid or short circuit to the earth is occurred by a dew condensation formed on the one-piece type cap 35 or the outer casing 21.
Patent Document 1: JP-A-10-275744